Treatment of iron or steel.



UNITED STATES PATENT OFFICE.

WILLIAM RICHARD HOIDGKINSON, OF BLACKHEA'IH, ENGLAND.

TREATMENT OF IRON OR- STEEL No Drawing.

To all whom it may concern:

Be it known. that I, VILLIAM RICHARD Honoxrxsox, a subject of the Kingof Great Britain, residing at 18 Glenluce road, Blackheath, in thecounty of Kent, England, have invented certain new and useful'Improvements in or Relating to the Treatment of Iron or Steel, of whichthe following is a specification.

This invention relates to the treatment of iron or steel and hasparticular reference to the carburizing or case-hardening of iron ormild steel, the chief object being to enable this result to be attainedin a simple, rapid and effective manner and to avoid the liability ofthe iron or steel, or article composed thereof, becoming deformed orotherwise rendered defective by being raised to an excessively hightemperature.

According to this invention the iron or steel is heated to anappropriate temperature in contact with or in an atmosphere of a mixtureof acetylene and ammonia gases.

In carrying the invention into practice the iron or steel is placedin amuffle or similar chamber which is heated to the'desired temperature andthe gaseous mixture of acetylene and ammonia is passed into the saidchamber, or materials which will yield the gaseous mixture areintroduced'directly therein. Thus, calcium carbid may be added to astrong ammonia solution in which case a mixture of the two gases,ammonia and acetylene, is produced, or a mixture of calcium carbid andammonium chlorid may be introduced into the heated chamber, the reactionwhich takes place in the latter case being represented by the followingequation:

The component gases of the gaseous mixture are preferably in about theproportion of two volumes of ammonia to one volume of acetylene. howeverbe employed, the only objection to proportions different from thoseabove stated being that the excess of one or other of the gases is tosome extent wasted; a

Specification of Letters Patent;

Any, other proportions may.

Patented Jan. 11, 1910.

Application filed August 29, 1907. Serial No, 399,624.

ture with ammonia prevents or checks mere decomposition of the acetyleneor depos1-' tion of carbon in the form of soot. It is probable thatcyanogen is formed and afterward decomposed, as it has been found thatthe iron or steel after treatment contains some nitrogen.

The steel produced by this process is much harder than ordinary casehardened steel Without chilling and the metal is hard ened to a muchgreater depth in a given time. In appearance it is, under themicroscope, of fibrous or net like structure as distinguished from thegranular structure of ordinary case hardened steel. This fibrousstructure 1s not always apparent in chilled steel but the characteristicappearance can be readily brought out by heating to a high temperatureand allowing it to' cool slowly.

The rate at which the iron or steel is being carburized or case-hardenedcan be ascertained and controlled by examining trial pieces, or byregulating the temperature or time of exposure. Thus, iron at atemperature of about 360 C and exposed to the gases for three or fourhours will become carburized to about an equal extentif exposed forabout ten minutes when the iron is heatedto 1000 C. As a furtherexample, it may be stated that a bar of mild steel of one half a squareinch in sectional area and containing .047 .of carbon when exposed tothe gaseous mixture for thirty minutes ata temperature of from 500 to600 C, is carburized to the hardness of steel containing about 1% ofcarbon.

When the result of the examination of test pieces indicates that thereaction is complete the iron or steel is removed from the furnace andapplied to the various purposes for which case-hardened or carburizediron or steel is preferable or essential, as for example in theconstruction of armor plates.

What ters Patent of the United States is I claim and desire to securebyLet 1. The process of carburiz'ing or caseto the conjoint action ofacetylene and ammonia gases.

2. The process of carburizing orcase llO hardening iron or steel whichconsists in subjecting the same, in a heated condition, to a mixture ofacetylene and ammonia gases such that upon ignition the resulting flameis luminous but not very smoky, substantially as described.

3. The process of carburizing or case' hardening iron or steel Whichconsists in subjecting the same, in a heated condition, to a mixture ofacetylene and ammonia gases the proportion of said gases beingsubstantially one part acetylene to two parts ammonia gas, substantiallyas described.

4. The process of carburizing or case hardening iron or steel whichconsists in subjecting the same at a temperature sufficiently high tonormally decompose acetylene gas, to a practically non-explosive mixtureof acetylene and ammonia gases.

In testimony whereof I allix my signature in presence of two Witnesses.

WILLIAM RICHARD HODGKINSON.

Witnesses ARTHUR H. Coorn, RALPH M. SAW.

